Function of Isolation Transformer

[fredster]

Techies :What is the specific function of a 1:1 Isolation transformer?

[Ken Layton]

As pertaining to commercial arcade games the function is solely to isolate the monitor's "hot" chassis from all other components in the cabinet and keep you from frying if you touch the chassis. Only the monitor is connected to the output side of the transformer and nothing else.

[fredster]

Isn't supposed to keep the AC at a steady 60hz?  Keep the spikes out so the monitor doesn't blink?

[Ken Layton]

No, the transformer was not designed as a voltage regulating/spike protecting unit.

[fredster]

I thought it was to keep the power "clean" and remove any stray spikes and static frequency interference.

You are saying that it isolates the power to the monitor from the power supply?  

The way you explained it the isolation transformer sounds more like a saftey feature rather than a functional part of the monitor. Then why does it say "isolation transformer required."

To prevent feedback from the HV unit to the rest of the system in case the monitor freaks?

[Ken Layton]

The isolation transformer has nothing to do with feedback or anything with the high voltage. It isolates the wall outlet voltage to keep it off the metal frame and ground connections of the monitor. It is a safety device for sure.

[menace]

would you guys mind if i added this exchange to the FAQ?  this seems to be a common misconception.

[SirPeale]

Not at all.  It needs to be answered a lot.

If you want to filter the power, get a power filter.  They're like five bucks or less.

[fredster]

Well I stand corrected.

 I thought it had more of a function than just isolation.  

The function is to isolate the monitor from the rest of the game so you won't be electrocuted in case of a short. It's not necessary for the monitor to actually work, it's a saftey feature.

I understand and thanks for the info.

[AndyWarne]

This subject is covered in some more detail on my monitor FAQ:
http://www.ultimarc.com/monfaq.html

Andy

[Ken Layton]

Yes, it is actually necessary for the monitor to work properly. If you connect the monitor directly to the wall power AC without an isolation transformer you will literally AND immediately damage the monitor's main pc board. Likely the power supply diodes will explode along with a couple of capacitors and maybe even the copper foil traces actually blow right off the board!

[MonitorGuru]

> "The function is to isolate the monitor from the rest of the game so you won't be electrocuted in case of a short"

It is not there solely for  "protection" or safety perse, and has NOTHING to do with protection from internal shorts. (e.g. a GFCI outlet in your kitchen/bathroom does that).

As Ken said, if you attach the monitor directly to the AC outlet, anything you connect to it will be blown up immediately upon connection, including yourself touching it.

The exact same principal applies to a standard consumer television set.

If you crack it open, and are stupid enough to plug it in and then touch a "though to be grounded" metal part like the mounting ears of the tube, you will get a 120 volt AC shock through you, and if you're lucky, you will survive and learn not to ever do it again.  Therefore on the insides of TV sets there are always stickers stating "attn: repair personel...unit must be isolated from mains for service".

If you plug the TV into an isolation transformer then it is safe to work on while live (barring of course the high voltage areas just like an arcade monitor).

Now you may ask..  "Hey... you can't be correct... I touch metal things on the outside of my TV set all the time, and in fact connect other components to it, including rabbit ears or a cable box!".

Yes, you are right.   However if you take a look at the insides of them, you will see there is a ceramic capacitor between the jack and the signal trace on the circuit board. This capacitor prevents voltage from going through but allows signals to travel correctly.   Expensive TV's sometimes use high priced things called opto-couplers. Basically it connects via light so there is a total separation of metal electrified traces, thus protecting the ports.

 
There are numerous reports of weekend hobbiests who wanted to add a headphone jack to the outside of a TV that didn't have one.  They usually wired it directly to the 2 terminals of the speaker, and then got a nasty shock when plugging in their headphones, or blow the TV or attached device if they attempt to ground the jack.  Yes, all because TV's, just like arcade monitors, run on what's called a "HOT chassis".

Search google for information regarding the reasons why isolation is needed to provide a differrent point of "ground / neutral" rather than earth ground.

[Hamselv]

This is... interesting.

I need to resize the screen on my Phillips 21GR2550 (G90AE chassis) for use with ArcadeVGA. I opened up the TV (with no power) and found the two pots on the carrier panel that I need to adjust, but I haven't gotten around to actually doing it (I need a mirror or a wife to stand in front of the TV and let me know when the picture is good).

The carrier panel is mounted with metal 'walls' standing at 90 degrees at the back end (closest to yourself when looking from behind the TV). These walls are permanently attached to the carrier panel and slides in and out along with the panel. I imagine they are primarily there to stiffen the PCB for when you slide it in and out when servicing the TV.

The carrier panel and these metal 'walls' are not hot in any way, are they? Except for the 'hatch'-marked areas on the PCB, of course. I am asking because one of the pots I need to trim is accessible only through a small hole in said metal 'wall'.

I can put in some pictures when I get off work.

Andy Warne (Ultimarc) mentions on his site that only older TVs had live chassis'. Could this be clarified a bit more? Is it possible that my TV already has an isolation transformer?

And, is it possible to use an isolation transformer from an old arcade machine as a general 'protection plug', using it as a bridge between the AC outlet and the device you are fiddling with?

[JasonF]

And, is it possible to use an isolation transformer from an old arcade machine as a general 'protection plug', using it as a bridge between the AC outlet and the device you are fiddling with?

Yes, as this is exactly how you would use an ISO.  Wire the secondary from the transformer into a "wall outlet", and then you can plug the television directly into it.  

Note that any transformer can be called an isolation transformer.  In most cases as used in arcades, it's a 1:1 (meaning that the voltage is not stepped up or down).  Some games in the USA stepped the voltage down to Japanese household levels (100V) using a 1.1:1 transformer (Nintendo and early Sega games, for example).  And if you get your transformer out of a cabinet in the UK, then you might have a 2:1 transformer in it.  The bottom line is that you'll need to make sure that the secondary output from the transformer is appropriate for your television.

If you repair a lot of televisions or monitors, then a great tool to have on your bench is a variable AC power supply.  This is basically just a variac, or variable transformer, that allows you to set the voltage to anything between 0VAC to usually under 150VAC.  Besides providing isolation, a variac is great for being able to supply 100VAC to monitors that need it (Nintendo Sanyo's for instance).  It's also good for monitors that pop fuses--instead of replacing fuse after fuse, just slowly turn up the voltage and observe the amperage draw--if it approaches the fuse rating before reaching full operating voltage, then you still have a problem.

Personally, I have the B&K 1655, but their other one (1653) would also be a great addition to any workbench.  Both show up on eBay all the time.

http://bkprecision.com/www/np_searchmodel7.asp?lf=AC+Power+Supplies

[AndyWarne]

Note that any transformer can be called an isolation transformer.

NO this is dangerously incorrect. If you go out and buy a step-down transformer from 240 to 110 volts for example, this will be an auto-transformer. It will not isolate!
Also Variacs are auto-transformers and do not isolate!!
The transformer must be explicitly sold as an isolation transformer to be one.
Also, all currently made TVs have grounded chassis. Live chassis TVs went out about 10 years ago. Otherwise you would not have any way to connect SCART or component video etc.

[MonitorGuru]

> "Also, all currently made TVs have grounded chassis. Live chassis TVs went out about 10 years ago. Otherwise you would not have any way to connect SCART or component video etc."

Not entirely correct. I've cracked a few made within the last 10 years that still have hot chassis.  The cheaper they are the more likely they are to have hot chassis yet. Since you mention SCART you may be in Europe which would be different than the states.

Also, as noted above, you definitely can have scart and other types of connectors and still have hot chassis.  All you need to do is isolate the inputs from the ground differential.  You can do this most of the time with simple capacitors, and the better sets would use opto couplers to bridge the gap.

ALWAYS assume a set is a hot chassis unless electrically proven otherwise.  You can NEVER hurt anything by running a set not requiring an isolation transformer through one anyway for that extra level of safety just in case you guessed wrong.

[JasonF]

NO this is dangerously incorrect. If you go out and buy a step-down transformer from 240 to 110 volts for example, this will be an auto-transformer. It will not isolate!
Also Variacs are auto-transformers and do not isolate!!
The transformer must be explicitly sold as an isolation transformer to be one.

I stand corrected on the auto-transformer (variac).  Looking inside the B&K 1655, I see that they do indeed have a separate ISO.

[JoeB]

If I take a power bar, and hack it to be as so:

OUTLET <-> ISO transformer <-> power bar

if I plug the TV into the power bar, would it be save to touch the chasis? Is the TV isolated?
Is this what repair people do?

[MonitorGuru]

If I take a power bar, and hack it to be as so:

OUTLET <-> ISO transformer <-> power bar

if I plug the TV into the power bar, would it be save to touch the chasis? Is the TV isolated?
Is this what repair people do?

Yes, however most repair people don't attach a multi-plug after the iso, just a single outlet, though there is nothing wrong with a power bar, but be aware that the iso transformer may have a maximum number of amp capability, and if you attempt to exceed it with multiple items plugged into a power strip after it you will end up blowing the transformer.  (Thats why in most games ONLY the monitor is attached to the iso, while the rest of the system, including old linear or new switch mode transformers AND flourescent lighting are directly attached to the mains to reduce the stress on the iso.)


And as far as if it is safe to touch the chassis... even if on an iso, you still need to take care and don't discriminately touch stuff.  When in doubt, whip out the multi meter and test to mains ground  neutral to be entirely certain there are no gotcha's.

Be aware that the anode ground of the tube attaches to the metal frame and mounting ears.  A bad contact of that wire/spring to the aquadag on the outside of the tube could cause sparking/arcing even though it is from a ground point.  Therefore you don't want to be touching more than you need, but at least you're protected somewhat once you have the iso in place.

[Blakey]

How does all this relate to PC monitors?

In my case, I have taken a ~2000 model panasonic 17", removed the outer case, cut a hole in a timber panel and mounted the screen in that using the ears on each corner. Due to space reasons I've left all casing off, am I likely to get fried if I touch the ears?

I haven't powered up yet, so I may as well ask before I do so.

[MonitorGuru]

Likely not to be fried. Most PC monitors have had isolation in them since they have so many signals comming into them, it was cheaper to isolate the chassis than it was to protect each signal line.

Even looking back to some early 80's Commodore monitors I've hacked for arcade use, they all had isolation built in.

Again, it does not hurt to use one if in doubt.   You could also use a multimeter (on AC 200 volt setting) to check if there is a voltage differential between the mounting ears and earth ground/outlet neutral.  If there is, then there is NOT isolation, if 0 volts, then the monitor is isolated.

You can usually find the isolation by looking for a little transformer mounted next to the power cord going in and the fuses.  It is a little bigger than the transformers used on PC modem cards, but much smaller than those used on arcade games, since all recent computer monitors use switch mode power supplies on them instead of linear transformer.

[fredster]

Boys, I want to share with you what MonitorGuru sent to me.  It's the explaination I was looking for.  Up until I read this, I didn't understand the fundamentals of AC power generation.  He makes it very very clear in this PM he sent, I thought it soooo good I had to share it with the group!  


Monitor Guru wrote:

Isolation means isolation of both hot and neutral from the earth ground/neutral.



You need to understand how electricity works and is fed to your home.

Basically high voltage wires only carry the "hot" line to your neighborhood transformer before it comes into your house.  The "return" line is in fact, the earth. It's set up this way at the power plant. This way they don't have to send electricity over 2 wires, one hot, one neutral. The power is instead sent over one wire, hot and the other wire is the earth itself.

Therefore before the electricity comes into your home, the neutral wire is physically attached into the earth...not to the power plant.  This neutral line, along with the hot wire come into your house.    Once in your house, a third line is added, a ground wire, which is connected to the water pipe comming into your home.

These three wires are then sent throughout your house to all outlets.  *TECHNICALLY* you only need 2 wires... HOT+Neutral  *OR* Hot+Ground, either way they form a complete circuit.

The addition of ground was done so that if there was a short, the power is returned to ground sooner (inside your home) rather than later (at the transfomer down the street).

Therefore testing a regular AC outlet will show that HOT to NEUTRAL = 120 volts.  HOT to GROUND *ALSO* = 120 volts, while NEUTRAL to GROUND should = 0 volts, if wired properly.  If you set the meter on ohm resistance however, you will find a significant resistance between neutral and ground, due to the longer wire run to the transfomer outside your house, which makes sense.

Okay, now that you know that, you can then see why a hot chassis can shock you.

A hot chassis means that electricity is directly connected to the main hot wire (as well as neutral) comming in. However all the metal on the monitor is electrified because it's forming a loop between hot and neutral.  If you touch the monitor as it's running not isolated... guess what... the electricity will always find the SHORTEST PATH TO GROUND.  Unfortunately that means you and not the neutral line.  Yes, if you are not standing on wet floor and not barefoot, you have a significant amount of resistance, greater than the copper neutral wire in the wall, but you will still pick up a shock. It may not be the full 120 volts/15 amps, but it definitely will be felt, and vary depending on humidity/etc..  

Okay... in this case, if you held a multimeter to any metal part of the monitor and touched the lead to the ground on an outlet, it should read 120 volts..  Touch the opposite lead to concrete floor and it will read a bit less but will not be zero volts.  Again, electricity wants to take the shortest, quickest route to ground since that is the return point being created at the electric plant itself.

Given this, if you put an isolation transformer on, you isolate the creation of power into it's own sealed loop (the secondary winding on the transformer).  Therefore there is no potential difference to earth ground.  It's not part of the loop.  Therefore if you now test a metal part against ground (or even neutral of an outlet) you should see 0 volts.  The only path to neutral is directly through the windings of the power supply and nothing else.  It's "isolated" from another power source.

[JoeB]

Given this, if you put an isolation transformer on, you isolate the creation of power into it's own sealed loop (the secondary winding on the transformer).  Therefore there is no potential difference to earth ground.  It's not part of the loop.  Therefore if you now test a metal part against ground (or even neutral of an outlet) you should see 0 volts.  The only path to neutral is directly through the windings of the power supply and nothing else.  It's "isolated" from another power source.

I have difficulty understanding this paragraph.

- Are you saying that w/o the transformer, the electricity flows from the hot wire to the chasis and out to the neutral/ground ?? If so, what stops it from short circuiting???
- This isolating transformer stops the chasis from being hot?
- How do the components continue on working if the chasis is no longer hot?
- If the iso transformer is there, what stops electricity from still going through you if you touch the chasis?

I think this is where most people have a problem understanding the isolating transformer.

[fredster]

Correct me please if I am wrong.  But from Monitor Guru's explanation, there is only one wire comming into the house from the power company.

It's "HOT".  If you look at a plug, there are 3 prongs.  The Black one, the white one, and the Green one.  The black one is the "HOT" wire.  The white one is the Neutral Wire, and the Green one is the "ground" wire.

Power flows from the black to the white wire.  The green one is a short path.  The white wire is attached to the earth either at the pole or near the electrical service (meter).  

If you have an isolation transformer, the transformer takes the power from an induction field of the white and black.  But now the power comes from the windings on the transformer, not by the hot connection/neutral.  If you put your hand on the hot chassis, you don't make a short from the black and white anymore, you are just shorting to the transformer.

It effectively separates the power from the earth.  That way you don't make a good connection from the black "hot" and the floor, which is the source of the white "neutral".  All you do is get between what the power transformer is making.  So you don't fry yourself by becoming a live wire.  

The green ground wire is just a short path to prevent overloads.

This also explains to me why people die by touching a power line that's on the ground.  You become a circuit by just touching ONE wire.  

I had always thought it took grabbing two wires to form the circuit from wire to wire with you in the middle.  You actually touch the hot and all of the planet is "Neutral".

[MonitorGuru]

Given this, if you put an isolation transformer on, you isolate the creation of power into it's own sealed loop (the secondary winding on the transformer).  Therefore there is no potential difference to earth ground.  It's not part of the loop.  Therefore if you now test a metal part against ground (or even neutral of an outlet) you should see 0 volts.  The only path to neutral is directly through the windings of the power supply and nothing else.  It's "isolated" from another power source.

I have difficulty understanding this paragraph.

- Are you saying that w/o the transformer, the electricity flows from the hot wire to the chasis and out to the neutral/ground ?? If so, what stops it from short circuiting???
- This isolating transformer stops the chasis from being hot?
- How do the components continue on working if the chasis is no longer hot?
- If the iso transformer is there, what stops electricity from still going through you if you touch the chasis?

I think this is where most people have a problem understanding the isolating transformer.

All electronics, including DC electronic connect various metal parts to their "ground". The difference with DC is that it is an ISOLATED (by nature of DC current) power source from the AC outlet, and therefore if you touch these parts you do not get shocked.  A monitor is no different. They don't take the time/expense/design changes to sparate the mounts for the frame from the neutral line in the monitor.. It's all "hot".

An isolation transformer doesn't change the electrical functionality of the chassis in any way. Electricity still flows identically. However what it DOES do, is separate earth ground from the monitor's idea of neutral.  Therefore it's on it's own power source completely separated from earth ground.   The reason it is no longer "HOT" is that there is 0 volt potential difference between the monitor and the earth.   If there was, then it is hot.  This doesn't mean there are no volts running through it, just that it has no potential to the ground.

A good way of understanding this is to pretend the monitor was in space and had a magical power source to it not connected to any planet   Now if you touch the monitor , you won't get shocked.  There isn't any voltage wanting to run from the monitor through you to what you're touching (because you're not touching anything).  Now, lets assume you are dumb and touch the neutral side of the isolation transformer and then touch the monitor at the same time.  Guess what? You now get shocked as the power will flow through you to meet back up with the inductance source--the isolation transformer.


Fredster's comments are exactly right: People die touching a SINGLE downed power line.  It's because it wants to return to the source of the power at the power plant, and unfortunately GROUND is how it does it. If you get in the middle of ground and power line, you're toast (Considering even in town, ac lines have 7,200 volts running through them to get to houses before they're reduced to 240 volts... ac wires in fields in the coutry will contain 155,000 to 700,000+ volts of power.... but then again it is also the amperage that kills you )


Check out this link: http://science.howstuffworks.com/power4.htm  for more info on how AC works and how neutral+ground = earth ground.


In my reply to Fredster that he posted, I glossed over some of the other reasons for the third ground wire, and that's covered on the howstufworks web site here: http://electronics.howstuffworks.com/question110.htm   It's not only about shortest path, but also to ground devices exteriors so that if an internal short does occur it shorts and blows a fuse/flips a breaker and doesn't shock you if you touch it.


No, I am not a power grid/or electrical engineering expert by ANY means, but was trying to get across in laymans terms why isolation transformers work.  I'm sure Ken Layton will be happy to point out any inaccuracies I have stated or add anything else.  

I definitely think most people have no idea why they need an isolation transformer because they just don't understand the difference between AC and DC power. (Just like it seems so many people believe they have to discharge and dismantle their entire arcade monitor just to pull it out of the cabinet to clean the cabinet and then replace.... caused by misinformation)  

[Halo]

Man .. reading this thread makes my head spin.  

So .. the ISO transformer is .. hmm .. I did have it .. once.

[SirPeale]

NOW I get it, but that's because I know how a transformer works.

Let's see if I can find an image to demonstrate:

Okay, no images, but here are some sites:

http://www.school-for-champions.com/science/actransformers.htm

http://www.energyquest.ca.gov/how_it_works/transformer.html

Since the two lines are seperate, there is no connection besides the electrons that pass from one coil to the other, the power is therefore 'isolated.'

[fredster]

I swear I will always use my isolation transformer and protect it from harm...

[JJS]

Yes, it is actually necessary for the monitor to work properly. If you connect the monitor directly to the wall power AC without an isolation transformer you will literally AND immediately damage the monitor's main pc board. Likely the power supply diodes will explode along with a couple of capacitors and maybe even the copper foil traces actually blow right off the board!

Absolutely.... I just fried a Nintendo Sanyo 2 weeks ago.... It took out a resistor and I had to solder a jumper wire accross to solder points because the trace fried.  Not too happy about it, but I'm a novice and am unfortunately lerning the HARD way.  I also learned from this experience that you need a isolation transformer that outputs 100V instead on 110V for that monitor.....

[JJS]

Again, it does not hurt to use one if in doubt.   You could also use a multimeter (on AC 200 volt setting) to check if there is a voltage differential between the mounting ears and earth ground/outlet neutral.  If there is, then there is NOT isolation, if 0 volts, then the monitor is isolated.

I'm really a newbie to all of this, and have finally gotten all of this through my think skull but have one more question:
I recently fried a Sanyo 20 EZV exactly as been described here ( see a recent post of mine).  I briefly talked to Bob Roberts about this and he said that if you do not use an isolation transformer and just plug it into the wall and happen not to plug it in backwards the chassis would get hot and you would get zapped - which seems to conform to what is being said here.  

Well, I happen to plug it backwards (my luck) and it of course blew the monitor out.  Why? What could isolating the power from the wall have to do with it?  My guess would be that with the Sanyo 20EZV's, they need 100V and I gave it 110V.

I'm really new to all of this and am trying to build a game from scratch.  I have 90% of all the parts, just need to make the cabinet and figure out all the wiring so that I don't ruin anything or blow myself up or start a fire or something.

Thanks,
Joe Schofield

[MonitorGuru]

>I briefly talked to Bob Roberts about this and he said that if you do not use an isolation transformer and just plug it into the wall and happen not to plug it in backwards the chassis would get hot and you would get zapped - which seems to conform to what is being said here.  

I'll defer this one to Ken Layton as I've never "tested" plugging something in "forwards" or "backwards" and seeing if there was a difference.

I tend to  believe Bob's comments are not technically accurate. Read below for what really happened:


>Well, I happen to plug it backwards (my luck) and it of course blew the monitor out.  Why? What could isolating the power from the wall have to do with it?  My guess would be that with the Sanyo 20EZV's, they need 100V and I gave it 110V.

If you JUST plugged the monitor in and had NOTHING else plugged into it (this means you did not have the wires from the game board for RGB+Sync+Ground) then you probably blew it solely due to the fact you sent 115-120 volts into it instead of the 100 it expected. It fried components by overvolting it.  As you stated on your other post, yes, Nintendo monitors were made in Japan and run on a lower voltage, and as such need a 1.1:1 step down transformer to reducethe ~115 volts to 100.


If however, you plugged it in and still had the wire harness attached to the game board, then as I stated in the previous thread, you ended up completing a circuit to GROUND on the game board and not ground in the outlet (neutral) and that's what fried it.

Again, Ken can probably attest to which occurence fried it first (overvolt or hot short) given your description of what failed.

[JJS]

Thanks for the explanation.  I believe that at the time, that was the only thing plugged in.  If I remember correctly, I was going to plug the monitor in then the PS for the PCB.  
About 2 weeks after that, I did the same thing again but with a Sharp XM1000 monitor (basically the same monitor).  Again, not knowing that it only needed 100V.  This time everything worked correctly and did not blow up.  The only thing I can think of is that I did not plug it in "backwards" (by this I believe to mean as far as plugging it in with regard to polarity - I think).  The only explanation I have for this would be the old saying "God takes care of the dumb"

Regards.
Joe

[DarkKobold]

Further on the isolation transformer - if you do not ground the iso, could it still kill the monitor? I didn't know that green needed to be attached to the case when I first plugged in my Iso.... I hope I didn't kill the monitor.

[MonitorGuru]

No, earth ground is not *needed* to be attached to the frame of the ISO or the metal of the monitor.

However, it typically is, again, to provide a safety factor so that if something shorts there can be protection, though you know the old saying, $75 in electronics will blow before the 75 cent fuse does.)


I've run many a machine (temporarily as it arrived that way when I purchased it) without an earth ground to the iso or the monitor frame without any ill effects  Ikj39@9201(iJhoiH@nlkK   (oops, that must be one of those ill effects )  



I think I have the definitive real world example that will help everyone understand isolation:

Think of an isolation transformer as a battery. pretend it's a 6 volt lantern battery, just 18 times more power/ac in real life).

If you take a wire and attach it to either the positive  or the negative of the battery or the lightbulb and then take the other end and stick it into the ground, your mouth, whatever.. You will not drain the battery, dim the light bulb or shock yourself.  The power is in an isolated loop with no desire to head towards earth ground because no power is going into the earth.

The same effect occurs with an isolation transformer.  The only way to be hurt is to directly break and then complete a circuit through yourself. (e.g. cut any wire and then hold each bare end).

[JJS]

I have a question on a specific isolation transformer that hopefully someone would know.  With regard to the ones used on the Nintendo Sanyo monitors , there seelms to be two wires being fed in to a block just in front of the transformer, but on the other side of the block, there's 3 wires feeding the transformer.  There's a brown wire that gets hooked into the transformer, but does not seem to go anywhere.  Is this a ground wire?  Please see the attached pic.  its not the greatest picture in the world, but it was the only way I could get it so it wasn't too large.

Thanks,

Joe

[DarkKobold]

So, wait one second, an isolation transformer is just a transformer that doesn't step down? .... eh.... eh.... Thank god I didn't take power in electronics, because otherwise this would be proof that my ECE degree was useless..

[JJS]

I have a question on a specific isolation transformer that hopefully someone would know.  With regard to the ones used on the Nintendo Sanyo monitors , there seelms to be two wires being fed in to a block just in front of the transformer, but on the other side of the block, there's 3 wires feeding the transformer.  There's a brown wire that gets hooked into the transformer, but does not seem to go anywhere.  Is this a ground wire?  Please see the attached pic.  its not the greatest picture in the world, but it was the only way I could get it so it wasn't too large.

Thanks,

Joe

sorry that the pic didn't show up (I don't know why - I must have messed it up).  But I think the extra wire is used if you were in Japan and didn't need the iso. to do a step down (1:1).  You would probably hook the hot to this other wire instead of where it is now.

[Trimoor]

These are great explanations as to why an iso will protect someone working on a monitor, but could someone answer, WHY, WHY is an iso required for an arcade monitor to funcion properly?

[MonitorGuru]

These are great explanations as to why an iso will protect someone working on a monitor, but could someone answer, WHY, WHY is an iso required for an arcade monitor to funcion properly?

It's explained above. But here it is in summary:

Without isolation, the power from the monitor will attempt to "return" through the ground wire (or actually any signal wire it found to have the lowest resistant path) of the video signal harness connected from the game board to the monitor.

This ground then will act as the return neutral path for the 120 volts AC after passing through the monitor, and subsequently go through all of the 5 volt DC paths on the game board and BOOM, you've just fried your game board, or it will go out through the wrong parts of the monitor board and blow up important components there too.


Oh and before anyone asks about "monitors not requiring an isolation transformer" it is because they ALREADY have an isolation transformer on it (usually a very very basic switch-mode one, like a computer power supply, so it appears as a tiny little transformer instead of a large heavy one).  If this isolation was bypassed, it too would fry the game board.

[AndyWarne]

These are great explanations as to why an iso will protect someone working on a monitor, but could someone answer, WHY, WHY is an iso required for an arcade monitor to funcion properly?

Actually, it isnt. If you consider the completely theoretical case in which the arcade cabinet would never have any exposed parts at all, so the PC is totally encased in the wooden cabinet, and the joysticks made of plastic, you could disconnect the ground from the PC and everything would work perfectly and be safe. This is exactly how the early TVs which old arcade monitors are based on, worked. There were no exposed parts so is was OK to make the chassis sit at either live or neutral (depending on which way the mains plug was inserted). This is totally unrealistic of course.
Once you get external controls involved, these just have to be grounded and cannot be connected to live/neutral for obvious reasons. So this sums up the isolating transformer function: it allows the chassis and anything connected, to be grounded instead of connected to live or neutral.
Actually the transformer frame and the monitor chassis must be grounded if an isolating transformer is fitted, otherwise they will build up a charge which could destroy attached components, apart from being unsafe.
Some people wonder why you can't just connect the monitor chassis to ground without using in iso. Well if you always made sure that the live and neutral were plugged into the wall correctly, this would actually work. BUT this should not be done because firstly it infringes electrical codes big time (ie connecting ground and neutral) and would rely on every wall outlet being wired correctly which many are'nt.